Up to now, there has been considerable interest in developing high energy density batteries using lithium as an anode. Lithium metal is particularly attractive as an anode active material of an electrochemical battery because of light weight and high energy density of the metal, for example, compared to a lithium-intercalated carbon anode, which increases the weight and volume of the anode to reduce the energy density of a battery due to the presence of non-electroactive materials, and other electrochemical systems having nickel or cadmium electrodes. A lithium metal anode or an anode mainly including lithium metal is lighter than batteries such as lithium-ion, nickel metal hydride or nickel-cadmium batteries, and provides an opportunity to configure a battery having a high energy density. These features are highly desirable for batteries for portable electronic devices such as cellular phones and lap-top computers where a premium is paid for low weight.
These types of cathode active materials for a lithium battery are publicly known, these materials include a sulfur-containing cathode active material including sulfur-sulfur bonds, and high energy capacities and re-chargeability are achieved from the electrochemical cleavage (reduction) and reformation (oxidation) of the sulfur-sulfur bonds.
As described above, the lithium-sulfur batteries using lithium and an alkali metal as an anode active material and sulfur as a cathode active material have a theoretical energy density of 2,800 Wh/kg (1,675 mAh), which is significantly higher than those of other battery systems, and have received attention as portable electronic devices due to an advantage in that sulfur is inexpensive due to the abundance in resources, and an environmentally-friendly material.
However, since sulfur used as a cathode active material of a lithium-sulfur battery is a non-conductor, there are problems in that it is difficult for electrons produced by an electrochemical reaction to move, sulfur leaks into an electrolyte during an oxidation-reduction reaction so that the service life of battery deteriorates, and furthermore, when an appropriate electrolytic solution is not selected, lithium polysulfide, which is a reduced material of sulfur, is eluted so that sulfur may no longer participate in the electrochemical reaction.
Thus, in order to minimize the amount of lithium polysulfide which is dissolved into the electrolytic solution and impart electric conductivity characteristics to a sulfur electrode which is a non-conductor, a technology in which a composite of carbon and sulfur is used as a cathode has been developed, but an elution problem of lithium polysulfide still cannot be solved.
Therefore, there is a high need for a technology to improve cycle characteristics by effectively blocking lithium polysulfide from leaking into the electrolyte during the discharge of a lithium-sulfur battery.